Early Warning of Destructive Ocean Currents

Harsh and complex metocean phenomena such as solitons and other strong highly variable ocean currents can seriously disrupt offshore exploration drilling and development operations.

Wallingford, UK

28 May 2010

Having been affected by such activity during a previous drilling programme, ENI Krueng Mane (Indonesia) commissioned Fugro GEOS to provide a real-time Soliton Early Warning System (SEWS) to aid drilling operations Northwest of Sumatra. ENI’s primary requirement was for the system to provide Drilling Engineers with a 10hrs warning window for the onset of strong currents.

“The client required a reliable and effective means of detecting solitons in real-time with a warning period long enough to prepare accordingly,” explains Gus Jeans, Consultancy Manager of Fugro GEOS UK. “A ’soliton’ is a particular type of short period internal wave in which the currents vary considerably over a time scale of a few minutes. Solitons cannot always be predicted using numerical models, so accurate predictions can usually only be achieved through observations. Solitons have been observed in many parts of the world, but have so far been recognised as a challenge to the offshore industry in a few key regions around Southeast Asia.”

A three phase project

The SEWS project was split into three distinct phases. The initial task was to provide a desk study based on Synthetic Aperture Radar (SAR) satellite imagery. This identified the key characteristics of solitons impacting the drill site, including propagation speed and direction. “This confirmed the need for an early warning system and provided the necessary information required to plan and deploy the SEWS moorings in the most effective way,” explains Martin Goff, Fugro GEOS Project Manager.

The most significant part of the project was the real-time current and soliton monitoring system. The platforms were Fugro OCEANOR Wavescan buoys fitted with Iridium data transmitters, Acoustic Doppler Current Profiler sensors (ADCPs) and temperature and conductivity sensors. Data were transmitted to a server receiving station and uploaded onto a dedicated, password protected web display, complete with accessible plots and data tables. The two Wavescan buoys gave a minimum warning period of 10-hours; the minimum time for appropriate action to be taken by the rig in the event of a soliton detection. The real-time data was monitored every 20-minutes around the clock by Fugro GEOS, with an Oceanographer on-call 24-hours a day to verify events and issue warnings.

The final part of the project involved the analysis of the measured data for future field development criteria and an additional soliton analysis of measured data to improve on the initial desk study.

Achievements of the SEWS project

An effective Soliton Early Warning System was deployed, providing real-time soliton monitoring to support rig operations. “Several solitons above the warning threshold were detected, we received prompt warnings from Fugro GEOS and took appropriate action,” says Carlo Baschenis, of ENI. “The SEWS system certainly helped avoid possible damage to the rig and subsea tooling. We would certainly use the system again if solitons posed a risk to safety and operations.”

As well as a real-time system for drilling operations, the SEWS system provided valuable data for any future site operations or field development, reducing the need for current meter deployments in the future.

Following the success of the SEWS system in the Andaman Sea, Fugro GEOS is now in discussions with clients for SEWS systems for soliton current detection offshore China.